Luis Lugo

Thermal conductivity and viscosity measurements of ethylene glycol-based Al2O3 nanofluids

The dispersion and stability of nanofluids obtained by dispersing Al2O3 nanoparticles in ethylene glycol have been analyzed at several concentrations up to 25% in mass fraction. The thermal conductivity and viscosity were experimentally determined at temperatures ranging from 283.15 K to 323.15 K using an apparatus based on the hot-wire method and a rotational viscometer, respectively. It has been found that both thermal conductivity and viscosity increase with the concentration of nanoparticles, whereas when the temperature increases the viscosity diminishes and the thermal conductivity rises. Measured enhancements on thermal conductivity (up to 19%) compare well with literature values when available. New viscosity experimental data yield values more than twice larger than the base fluid. The influence of particle size on viscosity has been also studied, finding large differences that must be taken into account for any practical application. These experimental results were compared with some theoretical models, as those of Maxwell-Hamilton and Crosser for thermal conductivity and Krieger and Dougherty for viscosity.

Enhancement of thermal conductivity and volumetric behavior of FexOy nanofluids

Homogeneous and stable magnetic nanofluids containing iron oxide nanoparticles, α-Fe2O3 (hematite) and Fe3O4 (magnetite) in ethylene glycol, were prepared at concentrations up to 25% in mass fraction. Commercial Hexagonal Scalenohedral-shaped α-Fe2O3 nanoparticles were selected while Fe3O4 nanoparticles were synthesized using a coprecipitation method. The products were characterized by transmission and scanning electron microscopy and x-ray diffraction. The thermal conductivity of both nanofluids was measured as a function of volume fraction and temperature. The results illustrate that the enhanced thermal conductivity of the nanofluids increases with volume fraction but is temperature independent. The experimental results show that both types of nanoparticles in this base fluid present no significant aggregation. These experimental values were also compared with theoretical models. Moreover, the density of these nanofluids was measured as a function of volume fraction, temperature, and pressure. The volu...

Rheological and volumetric properties of TiO2-ethylene glycol nanofluids

Homogeneous stable suspensions obtained by dispersing dry TiO2 nanoparticles in pure ethylene glycol were prepared and studied. Two types of nanocrystalline structure were analyzed, namely anatase and rutile phases, which have been characterized by scanning electron microscopy. The rheological behavior was determined for both nanofluids at nanoparticle mass concentrations up to 25%, including flow curves and frequency-dependent storage and loss moduli, using a cone-plate rotational rheometer. The effect of temperature over these flow curve tests at the highest concentration was also analyzed from 283.15 to 323.15 K. Furthermore, the influence of temperature, pressure, nanocrystalline structure, and concentration on the volumetric properties, including densities and isobaric thermal expansivities, were also analyzed.

Experimental excess volumes of organic carbonate+alkane systems. Estimation of the parameters of the Nitta–Chao model for this kind of binary mixture

Excess volumes at 298.15 K and atmospheric pressure of some organic carbonate+alkane binary systems have been measured using an Anton Paar 602 HP densimeter. For the first time, published data on excess enthalpies, excess volumes, excess Gibbs energies of the above-mentioned binary systems together with the vaporisation enthalpies and the molar volumes of the pure organic carbonates, were used to estimate the interaction parameters between the carbonate group O–CO–O and the methyl and methylene groups, CH3, CH2, respectively. The mean deviations between experimental and theoretical values were smaller than 6% for all the properties. We have also compared our results with those obtained by Garcia etal. with the Original, Tassios etal., Larsen etal. and Gmehling etal. versions of the UNIFAC model and with those obtained by Kehiaian etal. using the DISQUAC model.

Volumetric behaviour of the environmentally compatible lubricants pentaerythritol tetraheptanoate and pentaerythritol tetranonanoate at high pressures

Knowledge of proper lubricant selection and its handling can substantially influence the reliability of a refrigeration system. In this sense the awareness of several thermophysical properties of refrigerants, lubricants, and their mixtures under different conditions of pressure and temperature is highly important for designing refrigeration systems. Polyol ester oils have been proposed as lubricant candidates for refrigeration systems. In this work, we have studied the density of two polyol esters, pentaerythritol tetraheptanoate and pentaerythritol tetranonanoate, in the range 278.15 ≤ T/K ≤ 353.15 and 0.1 ≤ p/MPa ≤ 45. In addition, the behaviour of two other essential volumetric properties, namely the thermal expansion coefficient and the isothermal compressibility coefficient, as well as the internal pressure have been analysed.

Compressibilities and viscosities of reference and vegetable oils for their use as hydraulic fluids and lubricants

The use of biodegradable lubricants based on vegetable oils is receiving increasing attention, being an important area of research, in order to promote products with a reduced environmental impact during their entire life cycle. Compressibility is one of the key properties that should be taken into account to develop efficient hydraulic fluids and gear oils. The isothermal compressibility of four reference fluids, a sunflower base oil and a biodegradable oil up to 50 MPa and from 298.15 K to 373.15 K has been determined. For this aim an experimental device based on a vibrating-tube densimeter was used to obtain the density values. The density values at atmospheric pressure were correlated within an absolute average deviation of 0.07% with the Rackett equation whereas a modified Tait equation was used to correlate the experimental data over all temperatures and at higher pressures. The sunflower base oil analyzed in this work has a slightly lower compressibility than those of the reference oils for hydraulic and two stroke engines applications. Moreover, viscosities from 278.15 K to 373.15 K and the viscosity index (VI) were determined for all the analyzed oils using a SVM 3000 Anton Paar rotational Stabinger viscometer.

Modeling of Gas Solubility Data for HFCs–Lubricant Oil Binary Systems by Means of the SRK Equation of State

The Soave–Redlich–Kwong (SRK) equation of state (EOS) is used to describe vapor-liquid (VLE) and vapor-liquid-liquid (VLLE) equilibria of mixtures containing environmentally friendly refrigerants (hydrofluorocarbons, HFCs) and lubricant oils (polyalkylene glycols, PAGs and polyol esters, POEs) at high pressures. For refrigerants, pure component parameters are used as they were found in refrigerant properties computer program Version 6.0 of REFPROP. For the PAG and POE oils, they are either predicted by group contribution methods or obtained from thermodynamic data. Extension to mixtures is performed by using the conventional quadratic mixing rule with only one parameter for each binary pair. The binary parameters are regressed from VLE experimental data available in the literature and subsequently used for prediction of VLLE. All results of the calculations are discussed, and the necessary parameters for prediction of thermodynamic properties of these types of mixtures for the SRK EOS are presented. The computations were performed using phase equilibria software (PE2000).

Phase equilibria and pVT predictions for alkyl carbonate + n-alkane systems using equations of state

Abstract In this paper experimental data available in the literature on vapor–liquid equilibria, densities and excess molar volumes of dialkyl carbonate+ n -alkane mixtures on broad temperature and pressure ranges have been used in order to test four equations of state (EoS): Soave–Redlich–Kwong (SRK), Peng–Robinson (PR), Patel–Teja (PT) and Dohrn–Prausnitz (DP). For the pure components, when the critical parameters were not available in the literature, the group contribution method of Klincewicz and Reid was used to estimate the critical temperature and pressure. For dialkyl carbonate+ n -alkane mixtures we have determined the binary interaction parameter, k ij , using experimental vapor–liquid equilibria data and then with these parameters the pVTx values were predicted. The best correlations for VLE and predictions for the volumetric behavior were obtained with PR and PT equations.

Heat Transfer Performance of Functionalized Graphene Nanoplatelet Aqueous Nanofluids

The low thermal conductivity of fluids used in many industrial applications is one of the primary limitations in the development of more efficient heat transfer systems. A promising solution to this problem is the suspension of nanoparticles with high thermal conductivities in a base fluid. These suspensions, known as nanofluids, have great potential for enhancing heat transfer. The heat transfer enhancement of sulfonic acid-functionalized graphene nanoplatelet water-based nanofluids is addressed in this work. A new experimental setup was designed for this purpose. Convection coefficients, pressure drops, and thermophysical properties of various nanofluids at different concentrations were measured for several operational conditions and the results are compared with those of pure water. Enhancements in thermal conductivity and in convection heat transfer coefficient reach 12% (1 wt %) and 32% (0.5 wt %), respectively. New correlations capable of predicting the Nusselt number and the friction factor of this kind of nanofluid as a function of other dimensionless quantities are developed. In addition, thermal performance factors are obtained from the experimental convection coefficient and pressure drop data in order to assess the convenience of replacing the base fluid with designed nanofluids.

Analysis of the molecular interactions of organic anhydride+alkane binary mixtures using the Nitta–Chao model

Abstract The Nitta–Chao EOS group-contribution model, based on cell theory, is used to study the interactions of the organic anhydride+n-alkane binary mixtures. A database of excess enthalpies, excess Gibbs energies and excess volumes for this kind of mixtures, together with molar volumes and vaporization enthalpies of pure organic anhydrides, were used to calculate the characteristic parameters of the Nitta–Chao group-contribution model. In order to enlarge the database, the excess molar volumes at 298.15 K for the binary mixtures of pentanoic and hexanoic acid anhydrides with an n-alkane are reported. An analysis of the interactions is presented with the estimation of the changes of the mean numbers of contacts between the different groups during the mixing process. The influence of the dispersive and non-dispersive interaction energy parameters on the excess volumes and excess enthalpies is also presented. The model consistently describes the experimental data of organic anhydride+n-alkane mixtures, i.e. the excess volumes increase when the anhydride chain length decreases and when alkane chain length increases. The symmetry of the VE(x) curves and the sign and magnitude of the excess volumes are strongly dependent on the lengths of the alkane and of the organic anhydride.